What Is a Stock Keeping Unit (SKU)? Definition, Examples, and Best Practices

What is a SKU?

A Stock Keeping Unit, or SKU, is a unique alphanumeric code your business uses to track each product variant. A red size-medium t-shirt and a blue size-medium t-shirt are two SKUs, even if they share the same parent product. SKUs are internal: you create them and use them across your warehouse, ecommerce platform, and accounting books.

Example: a basic black hoodie in three sizes might have SKUs HOOD-BLK-S, HOOD-BLK-M, HOOD-BLK-L.

SKU vs UPC vs barcode

Three terms, often confused:

SKU: internal code you create. Unique to your business.

UPC: 12-digit Universal Product Code assigned by GS1. Used for retail scanning, same across all sellers.

Barcode: the visual representation of either a SKU or UPC. The lines under the numbers.

A SKU can be encoded as a barcode for warehouse use. UPCs are required if you sell in retail (Walmart, Target, Amazon Vendor). SKUs are required for your own warehouse and books regardless of channel.

How to write a good SKU

Strong SKUs share a few traits:

Short: 8 to 16 characters reads cleanly on a pick label

Readable: a picker can sound it out and recognize the product

Structured: same parts in the same order across every SKU (category, color, size, etc.)

Consistent: hyphens and capitalization match across the whole catalog

Avoids confusing characters: skip the letter O and the number 0, skip I and 1

Example structure: CATEGORY-PRODUCT-COLOR-SIZE. So HOOD-CREW-BLK-M reads as a black, medium, crew-style hoodie.

SKU examples by industry

Apparel: TSHIRT-CRW-BLK-M (t-shirt, crew neck, black, medium)

Beauty: SHMP-LAV-8OZ (shampoo, lavender, 8 oz)

Supplements: VIT-D3-5000-60CT (vitamin D3, 5,000 IU, 60 count)

Electronics: HDPH-BT-PRO-WHT (headphones, Bluetooth, pro, white)

Food: COFF-MED-12OZ-WHL (coffee, medium roast, 12 oz, whole bean)

Pick a structure and stick with it. Inconsistency between products is what kills SKU systems.

How many SKUs should a brand have?

Each unique combination of variant attributes is one SKU. A brand with 10 products in 5 colors and 4 sizes has 200 SKUs. A brand with 200 products in 1 color and 1 size has 200 SKUs. The product count is not the SKU count. Inventory complexity scales with SKU count, not product count.

Common SKU mistakes

Using the product name as the SKU (changes if you rename the product)

Auto-generating SKUs as random numbers (no information for the picker)

Inconsistent capitalization (HOOD-blk-M vs hood-BLK-m)

Including special characters that platforms strip (slashes, spaces, ampersands)

Reusing a SKU when a product is discontinued and replaced

Different SKUs in different systems for the same physical item

How SKUs flow through fulfillment

A SKU touches every system in the order path:

Order placed: Shopify or other platform passes the SKU on the line item

Order routed: WMS receives the SKU and finds the bin location

Picking: picker scans the SKU at the bin and at the pick station

Packing: SKU printed on the packing slip and shipping label

Inventory deducted: SKU count decremented in the WMS and synced back to the platform

When SKUs match across all systems, fulfillment is fast and accurate. When they do not, you get short-ships, mis-picks, and unhappy customers. See why inventory accuracy matters.

How 3PL Center handles SKUs

We track every SKU at the bin level in our WMS. Receiving scans confirm SKU and quantity at the door. Pickers scan SKUs at every step. Cycle counts run weekly on fast movers and monthly on the long tail. Stock counts sync back to your platform in real time, so what your store says is in stock matches what we have on the shelf. See more on 3PL inventory management.